1. Field of the Invention
This invention relates to an airborne multispectral imaging system and in particular to a computerized airborne multicamera imaging system with spatial resolution enhancement and extended dynamic range.
2. Description of the Related Art
There are increasing concerns about the environmental change of our earth and the effective management of human activities altering and using our planet. Modern terrestrial remote sensing, featuring digital spectral image data collection technologies, has been increasingly used for quickly and efficiently mapping, imaging and monitoring our planet earth from global scale to regional. The first commercial 1-meter resolution satellite, U.S. Space Imaging's Ikonos, was successfully launched in August 1999, joining the Landset, Spot, and other operational Earth observation satellites and providing 1-meter-resolution photographs of almost any place on earth. Aerial remote sensing platforms are indispensable and valuable adjuncts to the latest Earth observation satellites. New generations of smaller, lighter, power saving, cheaper and better hyperspectral/multispectral imaging systems are becoming operational to fly with diverse low-cost flying platforms in traditional light aircraft, balloons and airships to the latest unmanned aerial vehicles (UAVs). Quickly available higher spatial and spectral resolution airborne spectral images with extended dynamic range are broadly desired for regional, special and satellite-demanded ground truth remote sensing applications.
Modern hyperspectral, multispectral, and hyperspectral/multispectral multi-use airborne imaging systems for manned and unmanned aerial vehicles are capable of acquiring hyperspectral pushbroom scanning images, multiangle-multispectral pushbroom scanning images, and/or multispectral photographic framing images to satisfy a wide variety of remote sensing applications. Almost all these systems feature some sort of computerization, which not only permits bursting the acquired spectral images into computer memory for real-time analysis and saving them directly into the computer hard disk but also enables intelligent system control and automation.
Spatial resolution is one of the most demanding factors for remote sensing applications. Spatial resolution describes the fineness of detail that can be distinguished in an image. Higher resolution allows us to distinguish smaller objects. As the resolution linearly increases, amount of (or the market) for remote sensing applications could exponentially increase. For example, one-meter resolution satellite and airborne images can easily recognize cars and school buses, and can be used for road and pavement management, disaster relief control and many other city or regional plans. Sub-foot to inch-resolution airborne multispectral images, demonstrated in the system described herein, are desirable for many advanced innovative applications. From moose and wetland bird counting for wildlife management to under-canopy forestland monitoring, from village and golf course precision survey to town and country precision mapping, the applications are endless.
Dynamic range is another demanding aspect for remote sensing applications. The dynamic range is defined as the ratio of maximum measurable signal to minimum detectable signal. In remote sensing, it is the ability to discover dim features in the presence of strong, bright objects. Remote sensing produces wide area coverage and vast quantities of collected data. Very often the areas of interest include diverse dim and bright objects. Examples include searching for a downed light aircraft hidden in the forest or shallow water, monitoring the results of human controlled bush burning under a forest canopy, and evidence of illegal logging, where the faint and dim objects situated in the dark shadow areas of forest canopy are required to be detectable in the presence of very bright, very well illuminated canopies.
Resolution and dynamic range are so important that their enhancement and extension are generally considered as a key part of instrument system design.
In U.S. Pat. No. 5,790,188 issued to Xiuhong Sun on Aug. 4, 1998 and assigned to Flight Landata, Inc. of Lawrence, Mass., a variable interference filter imaging spectrometer (VIFIS) system is described which acquires ground track spectral images from air or space with a two-dimensional field of view and generates spectral imagery from three channels of synchronized video outputs. The synchronized video stream outputing from each camera is fed to a control and interface unit where a composite analog signal is formed from the individual output video signals for recording on an analog video recorder. A digital signal is also generated for recording on a computer disk. Control of the shutter speed of each of 3 cameras is provided.
In U.S. Pat. No. 6,211,906 issued to Xiuhong Sun on Apr. 3, 2001 and assigned to Flight Landata, Inc. of Lawrence, Mass., a computerized component, variable interference imaging spectrometer (C2VIFIS) is described for airborne remote sensing and data acquisition with a two dimensional field of view. Spectrally filtered video data is obtained from three synchronized CCD-imager modules or cameras wherein one imager module has a visible range variable interference filter on its surface, a second imager module has a near-infrared variable interference filter on its surface, and a third imager module has a bandpass filter attached to the imager. An alternating staring/scanning method is used to optimize a pushbroom hyperspectral image data set with a photogrammetric reference.
A computerized airborne multicamera imaging system (CAMIS) is described in a paper by Xiuhong Sun, James Baker and Richard Hordon entitled “Computerized Airborne Multicamera Imaging System” (CAMIS), Second International Airborne Remote Sensing Conference and Exhibition, San Francisco, Calif., 22-27 Jun. 1996. The CAMIS comprises a personal computer such as a Pentium 133 MHz computer which receives data from three synchronized CCD cameras with interchangeable narrow-band interference filters and a variable interference filter. Simultaneous, digital multichannel images are directly recorded onto SCSI drives without compression.
An improved computerized airborne multicamera imaging system (CAMIS) with four camera integration for remote sensing is described in a paper by Xiuhong Sun, James Baker and Richard Hordon entitled “Computerized Airborne Multicamera Imaging System (CAMIS) and Its Four-Camera Application”, Third International Airborne Remote Sensing Conference and Exhibition, 7-10 Jul. 1997, Copenhagen, Denmark. This improved CAMIS is a direct-sensor-to-computer imaging system which has integrated real-time positioning, a live moving map, and a live composite image display window for four cameras into a compact personal computer running under Windows NT. This paper also shows that a sequence of four channel CAMIS snapshots can be composed and mosaiked as a natural/NIR color composite pair with larger coverage, in which spectral characteristics beyond human eyes become easily recognized because of the large scale aerial multispectral viewing.
The present invention is a further improvement of the CAMIS having not only four synchronized progressive scan CCD video cameras with interchangeable narrow band interference filters but also spatial resolution enhancement and extended dynamic range.